1. Field of the Invention
The present invention relates generally to back-light systems for uniform illumination of large area displays. More particularly the invention concerns collimating back-light systems for displays such as liquid crystals displays and micro-electromechanical light valve displays.
2. Discussion of the Prior Art
Back-light assemblies provide a planar light source for transmissive displays. More common light sources used in display back-lighting are cold cathode fluorescent lamps and light emitting diodes.
Based on arrangements of light sources the back-light systems may be grouped either “edge-lit” or “direct-lit”. In direct-lit, back-light's plural light sources are evenly distributed along the display area and each of the light sources directly illuminates a small segment of the display. In order to achieve relatively uniform illumination the light sources are placed at a great distance from the display panel. This increases the depth of the display. Additionally, diffractive optical components and diffusers are placed between the light sources and the display panel. Each light source must align with the diffractive optical components.
The only positive feature of direct-lit systems is that light sources and associated heat is evenly distributed along the display area.
Edge-lit back-light systems comprise a light source, a thin, rectangular optical waveguide, a reflector or a diffuser at the back of optical waveguide and prism films mounted between the waveguide and the display panel.
The primary limitation of edge-lit back-lights is its incapability of illuminating a large size display. Efficient light coupling and concentrated heat generated from the light sources limit the size of the edge-lit back-lights.